Electric camera shutter with related controls

ABSTRACT

A camera having electrical circuitry for automatically determining the extent to which film in the camera is exposed. The circuitry includes an electromagnet for terminating an exposure upon deenergizing of the electromagnet. A DC voltage source is electrically connected to the electromagnet and there is also electrically connected thereto a supply of a rippled direct current having a weak AC component. This latter supply which takes place simultaneously with the supply from the DC voltage source counteracts an electromagnetic attractive force generated due to magnetic hysteresis of the electromagnet when the latter is deenergized.

United States Patent 1 1 Miyakawa et al.

[ Mar. 12, 1974 ELECTRIC CAMERA SHUTTER WITH RELATED CONTROLSlnvento'rs: Seinan Miyakawa, Tokyo; Hisawo Tanaka, F ukuoka-machi, bothof Japan Asahi Kohaku Kogyo Kabushiki Kaisha, Tokyo-to, Japan Filed: May9, 1972 Appl. No.: 251,762

Assignee:

Foreign Application Priority Data May 11, 1971 Japan 46-36974 u. s. C1.354/235, 354/38 1m. (:1. G03b 9/62, G03b 7/08 Field of Search 95/53 EB;317/123 References Cited UNITED STATES PATENTS 6/1972 Dick 317/123 A Q wv D- r-- 1 I i 7 L Primary Examiner-Samuel S. Matthews AssistantExaminer-Michael L. Gellner Attorney, Agent, or FirmSteinberg & BlakeABSTRACT A camera having electrical circuitry for automaticallydetermining the extent to which film in the camera is exposed. Thecircuitry includes an electromagnet for terminating an exposure upondeenergizing of the electromagnet. A DC voltage source is electricallyconnected to the electromagnet and there is also electrically connectedthereto a supply of a rippled direct current having a weak AC component.This latter supply which takes place simultaneously with the supply fromthe DC voltage source counteracts an electromagnetic attractive forcegenerated due to magnetic hysteresis of the electromagnet when thelatter is deenergized.

3 Claims, 4 Drawing Figures I I I I I l l I I I I l l I I l L.

PAIENTED MAR 1 2 I974 SHEET 2 BF 3 PAIENTEU "AR 1 2 1974 SHEET 3 BF 3ELECTRIC CAMERA SHUTTER RELATED CONTROLS BACKGROUND OF THE INVENTION Thepresent invention relates to cameras.

More particularly, the present invention relates to cameras providedwith circuitry for automatically determining the extent to which film inthe camera is exposed.

With cameras of this type there is a curtain type of shutter which has atrailing curtain which is released in order to terminate an exposure.The trailing curtain is held in its cocked position ready to be releasedto terminate the exposure by an electromagnet, and this electromagnet isconventionally deenergized in order to release the trailing curtain soas to terminate an exposure.

It is extremely important that the trailing curtain be released at theinstant of deenergizing of the electromagnet, but this type of operationis not achieved in practice because of the electrical characteristics ofthe electromagnet. Thus, it is conventional to energize theelectromagnet from a DC source. As a result upon deenergizing of theelectromagnet there still remains an electromagnetically attractiveforce due to magnet hysteresis which is peculiar to the magneticmaterial between the core of the electromagnet and the armature thereof.As a result of this latter factor, the trailing curtain is not releasedprecisely at the instant of deenergizing of the electromagnet, with theresult that there is an unavoidable inaccuracy in the extent to whichthe film is exposed with conventional cameras of this type.

SUMMARY OF THE INVENTION It is accordingly a primary object of thepresent invention to provide a camera which will avoid this drawback.

In particular, it is an object of the invention to provide a camera witha construction which will enable the trailing curtain to be releasedinstantaneously when the electromagnet is deenergized.

More particularly, the objects of the present invention includecircuitry which will avoid creation of the hysteresis which maintainsthe attraction between the core and the armature beyond the instant whenthe electromagnet is deenergized.

According to the invention the camera has circuitry for automaticallydetermining the extent to which film in the camera is exposed, and thiscircuitry includes an electromagnet means for terminating an exposureupon deenergizing of the electromagnet means. A DC voltage source iselectrically connected to the electromagnet means, and there is alsoconnected electrically thereto a means for supplying a rippled directcurrent having a weak AC component. Thus, this latter component togetherwith the supply from the DC voltage source will operate to counteractthe electromagnetic attractive force which is generated due to magnetichysteresis of the electromagnetic means when the latter is deenergized.

BRIEF DESCRIPTION OF DRAWINGS The invention is illustrated by way ofexample in the accompanying drawings which form part of this applicationand in which:

FIG. 1 is a partly schematic wiring diagram of circuitry forautomatially determining exposure;

FIG. 2 illustrates another embodiment of circuitry for achievingautomatic as well as manually-determined exposure;

FIG. 3 is a third embodiment of circuitry, this embodiment having avoltage source checking circuit; and

FIG. 4 is a fragmentary wiring diagram of a different embodiment ofcircuitry for introducing the factor of aperture size.

DESCRIPTION OF PREFERRED EMBOIDMENTS Referring to FIG. 1, the circuitryillustrated therein for determining the extent to which film in thecamera is exposed includes a DC-DC converter 1 having an input terminalla electrically connected by way of a conductor 30 to a DC voltagesource formed by the battery 17, this connection to the voltage sourcebeing provided by way of a main switch 16. By way of terminals 1b and1c, the converter 1 is connected to a circuit means 5 which serves tointroduce into the circuitry exposure-determining factors of the size ofthe exposure aperture and the speed of the film. This circuit means 5 isdescribed in greater detail below. However, it will be seen that thecircuit means 5 includes several variable resistor means which areconnected in parallel. As illustrated in FIG. 1 the circuit means 5 issupplied directly from the converter 1, and this arrangement is providedbecause the current consumed by the circuit means 5 remainssubstantially constant.

The DC-DC converter 1 may be constructed in any known way, and thedetails thereof do not form part of the present invention. Various typesof DC-DC converters are known. Such a converter as shown at circuit 3 ofUS. Pat. No. 3,625,124 or at circuit 7 in US. Pat. No. 3,605,00l issuitable for the present invention.

Two additional circuits are energized with the output of the converter1, and these two additional circuits have a variable current demand, sothat in this case a constant voltage supply means formed by voltageregulators 6 and 7 is used, these voltage regulators also serving tocompensate for thermal variations. Thus, by way of the output terminal1d, the converter 1 is electrically connected to the voltage regulator6, while by way of the output terminal Ie, the converter 1 iselectrically connected to the voltage regulator 7. These regulators aswell as the converter itself are suitably grounded, as illustrated inFIG. 1. Thus, the DC-DC converter 1 provides a circuit power source forthe circuit 5, this latter power source being independent of the powersource from the battery 17 which is somewhat increased or decreased toachieve output stability at the voltage regulators 6 and 7.

The circuit which is supplied from the voltage regulator 6 is alight-responsive circuit for converting the lighting conditions of theobject to be photographed into a corresponding electrical signal. Thislightresponsive means which is supplied by the voltage regulator 6includes a photosensitive element 3 which receives light from the objectto be photographed, this light first traveling through the objective ofthe camera before reaching the photosensitive means or element 3. Alsothe light-responsive means includes a diode 4 connected in series withthe photosensitive element 3 and acting as a logarithmic compressionelement.

The circuit which is supplied from the voltage regulator 7 is asignal-transmission means formed by the memory capacitor 9 which ischarged to an extent corresponding to the exposure-determining factors,and between the signal-transmission means 9 and the voltage regulator 7there is a logarithmic expansion circuit 8. This latter circuit isnormally grounded through the switch 10. This switch 10 is normallyclosed. When the shutter is opened, however, through an unillustratedmechanism the switch 10 is opened in synchronism with the opening of theshutter, so that the logarithmic expansion circuit 8 is at this timedisconnected from ground and is instead connected in series with thememory capacitor 9, upon opening of the shutter.

The several exposure-determining factors, namely the lightingconditions, the exposure aperture magnitude, and the film speed, areadded by the circuit whose output current charges the capacitor 9through the normally closed switch 11 until the terminal voltage of thecapacitor 9 attains the voltage level of the output from the circuit 5,this charging operation taking place while the switches 10 and 11 remainclosed. When-the tiltable mirror of the single lens reflex camera snapsupwardly beyond the path of light traveling along the optical axisthrough the objective, immediately prior to opening of the shutter, theswitch 11 simultaneously opens, with the switch 10 also openingsimultaneously with the opening of the shutter, as referred to above, sothat the charging of the signal-transmission means 9 with the signals tobe used in determining the exposure continues from the time when thecamera is directed toward the object to be photographed (actually fromthe time when the main switch 16 is closed) until the time when theswitch 11 opens.

The junction between the switch 11 and the signaltransmission means 9and a switching circuit means 12, referred to in greater detail below,are interconnected by way of a resistor 9a, so that through thisresistor the signal-transmission means 9 is connected with the switchingcircuit means 12. An indicating means 13, in the form of a suitablemeter, is connected in parallel with the switching circuit means 12.This switching circuit means 12 has at its output a transistor 14 whichis connected at its base to the remainder of the switching circuit means12, and through the transistor 14 the switching circuit means 12 isconnected to the voltage source 17 through a circuit which is thuscontrolled by the transistor 14. This latter circuit includes not onlythe energizing source 17 but also the main switch 16, which isautomatically closed during the initial increment of movement of theshutter-tripping plunger, before the shutter is actually tripped, aswitch 15 connected in series with the switch 16 and automaticallyclosed in a known way just prior to opening of the shutter as the mirroris snapped upwardly, and an electromagnetic means 2 which is connectedin series between the transistor 14 and the switch 15. Thiselectromagnetic means 2, when it is deenergized, will in a known wayrelease a trailing curtain of the shutter so that the trailing curtainwill run down to its rest position for closing the shutter. Thus, theelectromagnetic means 2, the switch 15, and the switch 16 are connectedin series between the transistor 14 and the battery 17.

The circuit 5 for adding the exposure-determining factors includes threevariable resistor means 19,20, and 21. These three variable resistormeans are connected in parallel between the terminals 1b and 1c of theconverter 1. It will be noted that the lightresponsive means formed bythe circuit which includes the components 3 and 4 is connected from thejunction 32 between the components 3 and 4 through a changeover switchmeans 18 to one or the other of the variable resistor means 19 and 20,so that in this way the exposure-determining factor of the lightingconditions at the object to be photographed is added to the otherfactors of the magnitude of the exposure aperture and the film speed,these three factors forming when added together the signal which issupplied to the signal-transmission means formed by the memory capacitor9. Thus, the signal according to the lighting conditions is added, inthe position of the parts shown in FIG. 1, by way of the switch 18 tothe aperture magnitude signal derived from the variable resistor 20which is connected in parallel with the variable resistor means 21 whichprovides the film speed signal, so that these three signals are combinedto form the output of the circuits which is delivered to the capacitor 9while energizing takes place by way of the independent constant voltagefrom the converter 1. The magnitude of the signals will depend upon theintensity of the light received by the photosensitive element 3 as wellas the positions of the movable electrically conductive components ofthe variable resistor means 20 and 21.

In this way the charging of the memory capacitor 9 is regulated inaccordance with the exposuredetermining factors.

The variable resistor means 20 is in the form of a potentiometer havinga slidable contact which forms the electrically conductive componentconnected to the switch 18 in the position of the parts shown in FIG. 1.This variable resistor means 20 is adapted to be used with an objectivewhich is automatic in the sense that it remains wide open and isautomatically stopped down to a preselected aperture just prior toexposure. Such objectives are well known. The objective has an aperturesetting ring which is turned to set the diaphragm for providing apredetermined aperture just prior to exposure. When this ring is turnedthrough an unillustrated transmission the slider of the potentiometer 20is shifted along the potentiometer to introduce into the circuit thefactor of the size of the exposure aperture. The sliding contact of thepotentiometer 21 is moved in the same way by way of a ring which is usedto introduce into the camera a value corresponding to the speed of thefilm which is exposed. In this way the variable resistor means 21 willintroduce a signal according to the film speed. The voltage controlfunction achieved with these potentiometers 20 and 21 is such that avariation of the preselected lens aperture value corresponding to onegraduation of the diaphragm setting ring and a variation of the filmspeed value corresponding to one graduation of the speed setting ringare maintained in correspondence with a variation of the light intensityby one incremental value such as one light value. Therefore, the outputof the circuit 5 is a voltage corresponding to the added informationderived from the light intensity at the object to be photographed, thepreselected aperture magnitude, and the film speed.

The diaphragm setting ring will, as is well known, determine the size ofthe aperture through which the film is actually exposed. However, thisring does not actually stop the diaphragm down to a positioncorresponding to the setting of the ring. This latter stopping down ofthe diaphragm is brought about automatically just prior to exposure, aspointed out above. For this purpose the diaphragm setting ring of suchan automatic objective is coupled to the sliding contact of thepotentiometer in such a way that a pawl or other motiontransmittingelement which moves together with the diaphragm setting ring extendsfrom the lens barrel of the objective into the interior of the camerahousing to transmit the motion to the sliding contact of thepotentiometer 20. Thus, in order to obtain this type of coupledoperation an automatic objective has a special structure fortransmitting the motion from the diaphragm setting ring to thepotentiometer.

However, it is also possible to use with a camera such as a single lensreflex camera a single stage lens which is commercially available andwhich must be manually stopped down to the required aperture since suchlenses do not have motion-transmitting elements which extend into thecamera for preliminarily setting a potentiometer to a setting whichcorresponds to a selected aperture. When such a non-automatic, manuallyadjustable objective is used with the camera, measurement of the lightwhich travels through the objective takes place in a restricted mannerthrough an aperture which has already been stopped down to the selectedvalue. During light measurement through such a stopped down aperture, itis not possible to obtain a useful function from the potentiometer 20and if the potentiometer 20 is used in determining the extent ofexposure there will be an unavoidable error, this error occurring ofcourse in the light measurement.

In the example shown in FIG. 1, the change-over switch means 18 normallyassumes a position engaging the contact 18b of the adjustable componentof the potentiometer or varialbe resistor means 19. The projection fromthe automatic objective, when the latter is mounted on the camera,serves not only to transmit movement from the diaphragm setting ring tothe adjustable component of the variable resistor means 20, but also todisplace the switch 18 to the position shown in FIG. 1 where it engagesthe contact 18a of the adjustable component of the variable resistormeans 20. Therefore, when using a non-automatic objective which must bemanually stopped down, the information or signal with respect to thelight intensity is added to the variable resistor 19. This secondvariable resistor means 19 has its movable adjusting component fixed bythe manufacturer after displacement to a position establishing acondition according to which the resistance value provided by way of thepotentiometer or variable resistor means 19 corresponds to theresistance which would be derived from the potentiometer 20 with thelatter short-circuited or bypassed.

In this conection, such a circuit arrangement is shown in the embodimentillustrated in FIG. 4 which differs from that of FIG. 1 only in that thepotentiometer or variable resistor means 20 is indeed provided with sucha bypass switch means 22, as referred to above. Thus, it will be seenfrom FIG. 4, that the bypass switch means 22 is connected between thepotentiometer 20 and the slidable contact thereof, so that when theswitch 22 is closed the potentiometer is bypassed in such a way that itachieves a constant voltage control function irrespective of theposition of the sliding contact. This switch 22 is a normally closedswitch. The motion-transmitting element carried by the automaticobjective will act on this switch 22 in order to open it only when suchan automatic objective is used. Therefore a manually adjustableobjective, which is to say an objective which must have its diaphragmmanually stopped down, will not influence the switch 22 which thusremains closed when using such an objective. Therefore in the closedposition of the switch 22 the potentiometer 20 provides a constantvoltage control function irrespective of the position of its slidingcontact. The resistance value achieved from the potentiometer 20 at thistime corresponds to that which is achieved from the potentiometer 19when its slidable contact is fixed by the manufacturer. Thispotentiometer 19 is useful in measuring the light even through anautomatic objective when the latter is in a condition where itsdiaphragm is actually stopped down.

Thus, with the above structure of FIGS. 1 and 4,

when the change-over switch means 18 engages the contact 18a, lightmeasurement is made through a wide open objective with the diaphragmsetting being preselected but not actually achieved'until automaticstopping down takes place just prior to exposure. On the other hand,when the change-over switch means 18 engages the contact l8b, itconnects into the circuit the variable resistor means which is adaptedto cooperate with an objective which must be manually stopped down withlight measurement taking place through the restriction provided by thestopped down diaphragm. Of course, this type of operation is alsoeffective even with an automatic objective after the diaphragm thereofis stopped down. It is to be noted that when the switch means 18 engagesthe contact 18b, the potentiometer 20 is disenabled even if the switch22 is opened, so that it is indeed possible to carry out lightmesaurement through a stopped down objective even if this objective isof the type which normally is automatically stopped down just prior toexposure. In other words it may sometimes happen that an automaticobjective is used in such a way that its diaphragm is already in astop-down condition during mesurement of light, and even in this casethe circuitry of FIGS. 1 and 4 will operate properly.

Thus, the exposure-determining factors supplied to the circuitry throughthe above-described signal supply means are stored in the form of anelectrical charge in the signal-transmission means formed by thecapacitor 9, and this capacitor 9 will temporarily hold this chargesince the switch 11 is opened immediately before the tiltable mirror issnapped upwardly. More specifically, any rays of light which happen topass through the objective after the mirror has snapped upwardly willnot reach the photosensitive element 3 so that the signal informationstored by the capacitor 9 is effectively prevented from being disturbedby signals which otherwise would continue to be provided by thephotosensitive element 3. This element 3 is in a position to receivelight which has passed through the objective and which is reflected bythe tiltable mirror, so that when the latter has swung upwardly beyondthe optical axis there is no longer any impingement of light on theelement 3 from the object which is to be photographed.

The switching circuit means 12 receives from the signal-transmission 9the signal coresponding to the addition of the exposure-determiningfactors as described above. This switching circuit means'l2 includes afield effect transistor 42 of high input impedance and a variableresistor 23 connected to the output terminal of the transistor 42, thisvariable resistor 23 also forming a potentiometer having a slidingcontact 24. This contact 24 forms part of a mechanism referred to belowwhich operates in a mechanical way to bring about an exposure time ofextremely short duration. The switching circuit means 12 furtherincludes a switching element 25 such as a thyristor for controlling thedeenergizing of the electromagntic means 2, and the sliding contact 24of the variable resistor means 23 is electrically connected to thecontrol electrode of the thyristor 25.

The switch is automatically closed just before the shutter is opened,while the tiltable mirror snaps upwardly, and at this instant the chargestored in the memory capacitor 9 is insufficient to render the switchingelement 25 conductive. Therefore, the transistor 14 remains in itsconductive state to maintain the electromagnet 2 in its energizedcondition. As a result the electromagnetic means 2 holds the elementswhich are required to be released in order to permit the shutter toclose, and thus these elements are prevented from operating even beforethe shutter opens, when the electromagnetic means 2 is energized byclosing of the switch 15.

The circuitry includes an additional field effect transistor 26connected in parallel with the field effect transistor 42. An indicatingmeans 13, in the form of a suitable meter such as an ammeter, isconnected to the transistor 26 in parallel with the output loadresistance 27 thereof. This indicating means 13 takes the form of anexposure meter structure in which an ammeter is utilized as theindicating instrument.

During transmission of the signal from the memory capacitor 9 to theswitching circuit means 12, the transistor 26 controls the electriccurrent which flows therethrough in accordance with the magnitude of thesignal. Thus, the transistor 26 will serve to reliably transmit thesignal stored in the capacitor 9 to the indicating means 13 in the formof a meter which is controlled in accordance with the magnitude of thesignal. This structure for giving an indication of the result of themeasurement of the light and the addition of the otherexposure-determining factors includes the transistor 42 of high inputimpedance which forms the input for the switching circuit means 12 andthe separate parallel-connected transistor 26 of high input impedance,so that the switching circuit operation with this circuitry iscompletely free of any electrical disturbance from the indicating means13 which otherwise would occur if the parallel connection through theseparate transistor 26 were not provided. Therefore the operation of theswitching circuit means 12, on the one hand, and the indicating means13, on the other hand, never interfere with each other. The value whichis indicated by the indicating means 13 corresponds to a shutter speed,and this indicating means 13 may be provided with a scale of shutterspeeds having graduations which cooperate with the movable pointer sothat the operator can directly read from the meter 13 the exposure timewhich will be provided by the circuitry, this exposure time beingdirectly measured in seconds on the scale at the meter. 13 andcorresponding to the magnitude of the signal which is transmitted to theswitching circuit means 12 by the signal-transmission means 9. Theindication given by the indicating means 13 is provided through asuitable switch which becomes closed automatically during the initialpart of the depression of the shutter-tripping plunger, before theshutter is actually tripped, so that after slight depression of theshutter-tripping plunger it is possible to measure at the meter 13factors such as the light at the object to be photographed, and theoperator may hold the shutter-tripping plunger in a partially depressedcondition in order to preliminarily see at the meter 13 the value of theshutter speed which will be provided by the circuitry if the depressionof a shutter-tripping plunger is continued to actually trip the shutter.

During the further depression of this shutter-tripping plunger thetiltable reflector is snapped upwardly in a known way, and the switch 11is automatically opened through a suitable transmission during theinitial part of the depression of the shutter-tripping plunger. Thememory capacitor 9 thus remains in its condition corresponding to thatwhich obtains just prior to opening of the switch 11. The tiltable mirorsnaps upwardly and then with the completion of the depression of theshutter-tripping plunger the shutter opens.

In synchronism with the opening of the shutter the switch 10 opens, andas this switch 10 opens the capacitor 9 is additionally charged throughthe logarithmic expansion circuit 8 from the voltage regulator 7. Thenthe input voltage of the switching circuit means 12 attains the level atwhich the switching circuit 12 transfers to a conductive state as thecharging of the capacitor 9 continues, and thus the switching circuit 12will suddenly transfer to a state of electrical continuity orconductivity. Therefore, the duration of the interval from the start ofthe additional charging through the logarithmic expansion circuit 8 tothe transfer of the switching circuit means 12 to the state ofelectrical conductivity corresponds to the timing signal whichdetermines the duration during which the shutter remains open, or inother words the duration of the exposure. The manner in which such atiming value is achieved is described in detail in copending applicationSer. No. 28,457, so that it is not described further.

It is possible to achieve control of relatively long exposures, forexample longer than l/500 sec., with extremely great precision throughthe operation of the above circuitry by corresponding regulation of theswitching level of the switching element 25. However, control of shorterexposures where the exposure time is at an extremely high speed range onthe order of l/l,OOO sec., for example, tends to be unstable due tofactors such as the time lag in the operation of the electromagnet 2. Amechanical shutter control mechanism may be operated preliminarily toachieve an effective control with extremely short exposure times incases such as the photographing of objects which move at high speed.Under these conditions control of the shutter by the electricalcircuitry which includes the switching circuit means 12 should beavoided so that this switching circuit means should not operateat thistime. This type of operation is achieved by deenergizing theelectromagnet 2 so that it will release the trailing curtain and thusterminate the exposure.

For this purpose, there is provided at the switching circuit means 12 acontrol means which controls the electromagnet in order to achieve, in amechanical way, an extremely short exposure time. This control meansincludes the sliding contact 24 of the variable resistor 23 which forthis purpose assumes a position displaced along the resistor 23 to alocation where a bleeder voltage is produced at the sliding contact 24in association with the change-over from electrical control tomechanical control. The arrangement is such that this bleeder voltage issufficiently positive and of such a magnitude that it is great enough totransfer by itself the switching element 25 to the conductive state atthe instant when the memory capacitor 9 is completely charged.

Thus, through the control achieved with a bleeder voltage resulting fromthe displacement of the contact 24 in association with the thyristor 25it is possible to achieve in a mechanical way a deenergizing of theelectromagnet 2 suitable for high speed operation where an extremelyshort exposure time is required.

During normal operation with longer exposure times, the switchingelement 25 transfers to its state of electrical conductivity and thevoltage on the anode side thereof drops sharply. A Zener diode 26 isinserted between the anode of the thyristor 25 and the base of thetransistor 14. As long as the thyristor 25 is in a nonconductive state,the Zener diode 26 is in its conductive state since the Zener diode 26is provided with voltage higher than its Zener voltage as a result ofenergizing of the Zener diode 26 from the voltage regulator 6. At theinstant when the element 25 transfers to its conductive state the Zenerdiode transfers to its nonconductive state since the input voltage tothe diode 26 will drop instantaneously at this time.

The transistor 14 transfers to its non-conductive state only underregulation of the magnitude of the control signal from the Zener diode26 which is connected to the control electrode of the tansistor 14, thisoperation taking place without any delay due to the counterelectromotive force generated when the electromagnetic means 2 connectedin series with the switching transistor l4 and serving to initiate theshutter-closing operation is deenergized. More specifically,thistransistor 14 transfers completely to its state of electricaldiscontinuity when the control signal to the transistor 14 isinstantaneously eliminated by the Zener diode 26 according to the signalfrom the switching element 25 at the instant when the latter becomesconductive. In this way the electromagnetic means 2 becomes deenergizedso that the trailing curtain is released from the holding effect of theelectromagnetic means 2 and starts to run in order to terminate theexposure by closing the shutter.

The circuitry provides a highly effective operation of theelectromagnetic means 2. This electromagnetic means 2 which has a highpower requirement is energized by way of the switch 15 just prior toopening of the shutter. The instant when the electromagnetic means 2 isenergized is selected in such a way that the duration of operation ofthe electromagnetic means 2 is reduced to a minimum. Therefore, theswitch 15 is not closed until the final moment before opening of theshutter, so that in this way the electromagnetic means 2 will reliablyhold the trailing curtain but at the same time will be maintainedenergized for a minimum duration. Accordingly, it is important to reduceto a mini- 'mum the time lag from the instant of closure of the switch15 to activation of the electromagnetic means 2. This result iseffectively achieved by supplying a large quantity of electricity to theelectromagnetic means 2. The battery 17 itself, however, has an internalresistance, with the result that it is difficult to provide a largequantity of electricity instantaneously. With the circuitry disclosed inFIG. 1, however, a capacitor 40 is connected through the main switch 16in parallel with the battery 17, and the capacitor 40 will have itsdischarge circuit established through the electromagnetic means 2 uponclosing of the switch 15. Thus, the

capacitor 40 forms a means for supplying to the electromagnetic means 2power in addition to that which is derived directly from the battery 17upon closing of the switch 15. Prior to closing'of the switch 15 the capacitor 40 is preliminarily charged from the battery 17 through the mainswitch 16 which is closed prior to closing of the switch 15. Thus, thecharge which has been stored on the capacitor 40 is discharged to theelectromagnetic means 2 at the instant when the switch 15 closes and theelectromagnetic means 2 is accordingly sufficiently energized by theadditional energy from the capacitor 40 as well as the energy from thebattery 17 to achieve an instantaneous activation of the electromagneticmeans 2. In this way the above time lag is very substantially reduced.

In addition, while a DC current is supplied to the electromagnetic means2 from the battery 17, a feeble AC component is applied to the circuitwhich energizes the electromagnetic means 2 from the DC-DC converter 1byway of the circuit which connects the battery 27 and the converter 1to each other, so that in this way a rippled direct current composed ofan AC output and'the output from the battery 17 is supplied to theelectromagnetic means 2. This rippled current effectively acts upon theelectromagnetic means 2 when the transistor 14 is turned off. The rippleform of current acts so that it is possible for an electromagneticallyattracive force generated due to magnetic hysteresis of electromagneticleectromagnetic means 2, upon deenergizing thereof, to be rapidlycounteracted by the ripple current as the switching circuit means 12transfers to the electrically conductive state and the transistor 14completely transfers to the electrically non-conductive state.Accordingly, upon deenergizing of the electromagnet 2, its holdingeffect on the trailing curtain is immediately given up and shutterclosing takes place instantaneously without any possible delay of thetype referred to above.

Thus, this circuitry for controlling the electromagnetic means 2 isuseful to reduce the time lag with respect to the moment when theelectromagnetic means 2 is energized as well as the time lag withrespect to the instant when the electromagnetic means 2 is deenergized,with time lags at both of these instants being reduced to a minimum soas to bring about a highly effective precision in'the operation.

In the embodiment described above the memory capacitor 9 is charged withthe output from the exposuredetermining factor adding circuit 5, and theexposure time is automatically determined according to the factor oflight intensity and the additional factors added by the circuit 5. Withthe embodiment of FIG. 2, the

switch 11 has the form of a change-over switch serving to selectivelyconnect into the circuit either the signalsupply means formedby thecircuit 5 and the lightresponsive circuit or an additional manuallyoperable signal-supply means formed by components 30-32 and connected tothe contact 1 1b of the change-over switch 11 of FIG. 2. The contact 11aof this change-over switch serves to transmit to the circuitry thesignals from the signal-supply means referred to above.

The manually operable signal-supply means 30-32 supplies a bleedervoltage output terminal 32 of the bleeder circuit 31 which is connectedto its own independent power source 30. The output terminal 32 ismovable relative to the bleeder resistance 31 so that the output voltagecan be manually determined. This manual determination of the magnitudeof this output voltage may be brought about by turning a suitable dialwhich is displaced in accordance with shutter speed graduations.

Thus, when the operator selects'to manually determine the exposure time,the switch 11 will be placed in engagement with the contact 11b, and nowthe capacitor 9 is charged to the level of thebleeder output voltage ofthe manually operable signal-supply means. When the bleeder outputvoltage is that resulting from operation in accordance with a selectedshutter speed graduation, the information or signal stored in thecapacitor 9 takes a value corresponding to this graduation and theselected shutter time corresponding to the selected graduation isachieved by additional charging in precisely the same way as duringautomatic control in the manner described above. In this way it ispossible to achieve with the embodiment of FIG. 2 a manually selectedexposure time while utilizing only a minimum amount of additionalstructure with the same controls, except for the signal supply means,being used both for automatic and manual exposure time determination.

The embodiment of FIG. 3 corresponds to those described above except forthe following differences. This emboidment includes a manually operableswitch 33 for opening and closing a checking circuit means capable ofchecking the condition of the voltage source 17.

' The normally open manually operable switch 33 serves to connect thebattery 17 to a resistor 34 of the checking circuit, this resistor 34being connected in series.

with a resistor 35 which in turn is connected with a diode 36 insertedin a forward direction with respect to the battery 17 which serves as aDC power source. These components of the checking circuit means areconnected in series between the battery 17 and the input terminal 13a ofthe indicating means 13. The checking circuit means further includes athermal compensating element 37 and adjusting resistances 38 and 39which are connected in parallel with the resistance 35, the diode 36,and the indicating meter 13 so as to achieve in this way a voltagechecking circuit for determining the condition of the battery 17 as theDC power source.

During checking of the voltage of the battery 17, the switch 33, whichnormally remains open, is manually closed. Of course, before closing theswitch 33 the main switch 16 is opened so that there will be nointerference with the checking of the condition of the battery 17 fromthe remainder of the circuitry. Closing the switch 33 initiates theenergizing of the indicating means 13 through the resistances 34 and 35and the diode 36 from the battery 17, so that the voltage of the battery17 may be reliably checked through reading this voltage which isindicated at a suitable scale of the meter 13 under regulation of thethermal compensating element 37. The diode 36 provided for checking ofthe voltage of the battery 17 as a DC power source is inserted in theforward direction with respect to the battery 17 so that the operationof the voltage checking circuit will have no influence on the operationof the indicating means 13 when the switch 33 is opened. Thus the samemeter 13 can be used for preliminarily indicating to the operator theexposure time which will be automatically achieved, as pointed outabove, as well as for battery checking purposes, without the checkingcircuit having any influence on the meter 13 when the switch 33 is open.Therefore, during measurement such as light measurement to control theelectric shutter the battery checking circuit will have no undesirableinfluence as a result of the diode 36.

Thus, the above circuitry assures a highly reliable operation byproviding the above checking circuit which enables the battery 17 to bemaintained in proper operating condition, as well as by providing amulti-source system formed by the DC-DC converter 1 and the voltageregulating means 6 and 8 in each load circuit which is likely to bethermally influenced in an undesirable manner.

What is claimed is:

1. In a camera having circuitry for automatically determining the extentto which film in the camera is exosed, said circuitry includingelectromagnetic means for terminating an exposure upon deenergizing ofsaid electromagnetic means, a DC voltage source electrically connectedto said electromagnetic means, and means for simultaneously supplying tosaid electromag netic means a rippled direct current having a weak ACcomponent so that the latter together with the supply from said DCvoltage source counteract an electromagnetic attractive force generateddue to magnetic hysteresis of said electromagnetic means when the latteris de'energized.

2. The combination of claim 1 and wherein said means for supplying saidrippled current is a DC-DC converter.

3. The combination of claim 2 and wherein a transistor is electricallyconnected to said electromagnetic means, a switching circuit meanselectrically connected to said transistor for controlling the latter todeenergize said electromagnetic means, and signal-transmission meanselectrically connected to said switching circuit means for transmittingto the latter exposuredetermining signals for controlling said switchingcircuit means to terminate conductivity of said transistor to deenergizesaid electromagnetic means.

UNITED STATES PATENT OFFICE '2 CERTIFICATE OF CORRECTION Patent No. 3,797 028 Dated March 12 1974 lnventofls) Seinan Miyakawa and HisawoTanaka It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

In 'the heading the name of the assignee should be: I

Asah-i Kogaku Kogyo Kabushiki Kaisha Signed and sealed this 29th day ofOctober 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM PO-1050 (10-69) I uscoMM-Dc 60376-F'69 U.5. GOVERNMENTPRINTING OFFICE: I910 0-366-3SL Patent No. 3,797,028 Dated March 12,1974 Inv t r( Seinan Miyakawa and Hisawo Tanaka It is certified thaterror appears in the aboveidentified patent and that said Letters Patentare hereby corrected as shown below:

In the heading the name of the assignee should be: 4

Asahi Kogaku Kogyo Kabushiki Kaisha Signed and sealed this 29th day ofOctober 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents PC4050 uscoMM-oc wan-Poo [L5, GOVERNMENT PRINTING OFFICE i I".D36-3!"

1. In a camera having circuitry for automatically determining the extentto which film in the camera is exosed, said circuitry includingelectromagnetic means for terminating an exposure upon deenergizing ofsaid electromagnetic means, a DC voltage source electrically connectedto said electromagnetic means, and means for simultaneously supplying tosaid electromagnetic means a rippled direct current having a weak ACcomponent so that the latter together with the supply from said DCvoltage source counteract an electromagnetic attractive force generateddue to magnetic hysteresis of said electromagnetic means when the latteris deenergized.
 2. The combination of claim 1 and wherein said means forsupplying said rippled current is a DC-DC converter.
 3. The combinationof claim 2 and wherein a transistor is electrically connected to saidelectromagnetic means, a switching circuit means electrically connectedto said transistor for controlling the latter to deenergize saidelectromagnetic means, and signal-transmission means electricallyconnected to said switching circuit means for transmitting to the latterexposure-determining signals for controlling said switching circuitmeans to terminate conductivity of said transistor to deenergize saidelectromagnetic means.